The present invention relates to a multiple speed split-phase induction motor and particularly to an induction motor having first and second run winding means and a starting winding means which is disconnected as the motor reaches or approaches operating speed.
A.C. induction motors are widely used in industrial, institutional and domestic applications. Single speed induction motors are constructed with a run winding connected in parallel with a starting winding. The starting winding may be connected with a phase shift capacitor or other impedance or may be specially wound to increase the starting torque of the motor. A centrifugal switch unit or an electromagnetic switch unit is generally connected in circuit with the start winding to disconnect the start winding at a selected speed, after which the motor operates with only the run winding connected. Although centrifugal and mechanical switches have been employed for many years, solid state switches devices have more recently been provided in place of the centrifugal switch. For example, General Electric application note 200.35, page 16, discloses an A.C. split-capacitor start motor in which a starting winding is connected in parallel with the running winding. The starting winding circuit includes a starting capacitor and a solid state switch shown as a "Triac". The solid state switch has a gate circuit coupled to the incoming power supply lines through a current transformer. The solid state switch is gated on only until the motor approaches running speed and then turns off to disconnect the start winding with the motor current at the normal operating level. The solid state switch replaces the conventional centrifugal switch or electromechanical relay. In either instance, the cut out switch is designed to open at a selected speed, thereby removing the starting winding and maintaining motor operation under efficient operating conditions with only the running winding connected to the power lines.
As more fully enclosed in the present inventor's copending application, entitled "Multiple Speed Induction Motor" filed on even date herewith, certain applications may demand different but constant speeds and a particularly simple but reliable winding and switch control for a dual winding and speed motor having a capacitor in series with the start winding is disclosed. The inventor's copending application discloses a unique combination of a first and second solid state switches controlling respectively, a first run winding and a start winding in combination with a mechanical or electromechanical type switch to control the selectively connecting of the start winding and one of the two run windings into circuit. Other multiple speed induction motors have been suggested in which the connection of a winding means, which is wound in different pole arrangements, is selectively connected in circuit by a selection switch and a centrifugal switch to permit operation of the motor at different speeds and with a single start winding unit, as more fully discussed in such application.